1. Field of the Invention
The present invention relates to a system with a 1+1 switching function, applied to a synchronous communication network.
2. Description of the Related Art
A 1+1 switching function (1+1 MSP) based on ITU standards performs switching by transmitting and receiving K1 and K2 bytes provided in the overhead of the data frame in an SDH (Synchronous Digital Hierarchy) or SONET (Synchronous Optical NETwork) network as bytes for monitoring and controlling between an opposite apparatus and an own apparatus. In this case, the settings of the own apparatus are known, but the settings of the opposite apparatus are unknown, since in the K1 and K2 bytes there are no Revertive/Non-Revertive mode settings (in order to simplify, hereinafter revertive and non-revertive are called xe2x80x9crevxe2x80x9d and xe2x80x9cnon-revxe2x80x9d, respectively) and uni-directional/bi-directional mode settings (in order to simplify, hereinafter uni-directional and bi-directional are called xe2x80x9cunixe2x80x9d and xe2x80x9cbixe2x80x9d, respectively) in the conventional North American SONET specifications. As a result, some failure occurs when the apparatuses are connected. (For details of K1 and K2 bytes, see ITU Recommendations G783.)
FIG. 1 explains the concept of a 1+1 MSP.
In a communication network where station A and station B being terminal stations are opposed, stations A and B comprise multiplexers 600 and 602 for multiplexing and demultiplexing received signals and transferring to signal processing units located at a latter stage (not shown in the diagram), and optical transmitter-receiver units 604 and 605 connected to optical transmission lines, for transmitting and receiving light beams. A running (work) line and a stand-by (protection) line each consist of a pair of an upward line and a downward line between the optical transmitter-receiver units 604 and 605 of stations A and B. Switches 601 and 602 are provided on the receiving side of the optical transmitter-receiver units 605 and 605, respectively, in stations A and B, and the switches 601 and 602 are to switch (bridge) the work and protection lines when a failure occurs. A switch for automatically preforming this bridging using the above-mentioned K1 and K2 bytes is called an xe2x80x9cAPS (Automatic Protection Switch)xe2x80x9d.
The configuration in FIG. 1 shows a 1+1 bridging function, and one protection line is provided for one work line. In a 1+1 MPS the transmitting side always continues to transmit the same signal in both the work line and the protection line, and the receiving side can receive the same signal by bridging the lines when a failure occurs. On the other hand, a bridging method in which the transmitting side does not always transmit the same signal to both lines, and starts transmitting a signal when the receiving side bridges the lines, is called a 1:1 MSP. Although in a 1:1 MSP one protection line is provided for one work line, a bridging method in which one protection line is provided for a plurality (N pieces) of work lines is called a 1:N MSP.
The above-mentioned rev mode and non-rev mode differ in whether or not a bridged protection line is bridged back the original work line when the failure is repaired. That is, in the case of a rev mode, the bridged protection line and the original work line are bridged back when the failure is repaired, and in the case of a non-rev mode the bridged protection line and the original work line are not bridged back. In the case of a uni mode, for example, when a failure is detected in station B, only on the receiving side of station B are the work line and a protection line bridged, and station A does nothing. On the other hand, in the case of a bi mode, when a failure is detected in station B and the work line and a protection line are bridged, this information is also transmitted to station A, and in station A too, the work line and a protection line are bridged.
FIGS. 2 through 9 explain the problems caused by K1 and K2 bytes without the settings of a rev or non-rev mode, and a uni or bi mode.
FIGS. 2 through 5 show the case where a terminal station with a rev mode and a terminal station with a non-rev mode are opposed, and FIGS. 6 through 9 show the case where a terminal station with a uni mode and a terminal station with a bi mode are opposed. In these diagrams a 1+1 MSP is presumed, and the diagrams are indicated in a 1:N compatible mode. Although an optimized 1+1 MSP based on the above-mentioned ITU Recommendations differs from a 1:N MSP in the way of using the K1 and K2 bytes set in the overhead of a data frame in an SDH or SONET network, the 1:N compatible mode of a 1+1 MSP means that in a 1+1 MSP K1 and K2 bytes are used in the same way as in a 1:N MSP.
FIG. 2 explains the case where the own station is in a uni and rev mode, and the opposite station is in a uni and non-rev mode.
When there is no failure, a signal in which an NR (No Request) and xe2x80x9c0sxe2x80x9d are respectively assigned to K1 and K2 bytes, is transmitted from each terminal station. That is, there is no request for an APS. In the same way, an NR is transmitted from the opposite station too. In this way, when there is no failure, the NR continues to be exchanged between the own station and the opposite station. When a failure is detected in the work line of the own station, an SF (Signal Failure) is set in the K1 byte and is transmitted to the opposite station. This indicates that a failure has occurred in a work line for transmitting signals from the opposite station to the own station. Therefore, when receiving an SF from the own station, the opposite station sets in the K2 byte a line number for commanding which protection line to use in order to bridge the work line, and transmits the line number to the own station. When receiving this line number, the own station bridges the work line and a protection line of the line number designated in the K2 byte which is transmitted from the opposite station, sets information that the work line is in a status of failure in the K1 byte as an SF, and transmits the information to the opposite station. At this time, although the work line for transmitting signals from the opposite station is out of order, the protection line also transmits the same information, and both the own and opposite stations always use the protection line to receive the K1 and K2 bytes. Accordingly, even if there is any failure in the work line, the K1 and K2 bytes are normally received. It is because bridging is meaningless if there is also a failure in the protection line when there is a failure in a work line, and the protection line is presumed to be normal when the bridging is performed so that a protection line is used to transmit and receive K1 and K2 bytes in this way. While the protection line is used, from the own station an SF continues to be transmitted, and the line signal of the protection line continues to be transmitted from the opposite station. When it is detected on the own station side that the failure of the work line is repaired, the protection line is bridged back over to the work line, and an NR is transmitted to the opposite station. When the opposite station has received the NR, the opposite station judges that the work line is restored, and also transmits an NR to the own station. In this way, when bridging and bridging-back due to a failure are performed on the own station side with a uni and rev mode, there is no problem.
FIG. 3 explains the case where the own station is in a uni and non-rev mode, and the opposite station is in a uni and rev mode.
In this drawing too, when there is no failure in both the own and opposite stations, a K1 byte is transmitted as an NR consisting of xe2x80x9c0sxe2x80x9d. When there is a failure in the own station, an SF is set in the K1 byte in the own station, and the K1 byte is transmitted to the opposite station in the same way as described in FIG. 2. When receiving the K1 byte, the opposite station sets a line number for a protection line in the K2 byte, and transmits the K2 byte to the own station. The own station bridges the work line and a protection line according to the command of this line number. Since a protection line is used to transmit and receive K1 and K2 bytes as described above, there is no problem in the transmission of the K1 and K2 bytes even when there is a failure in the work line. After bridging the work line and a protection line, the own station sets an SF in the K1 byte in order to indicate that the work line is out of order, and transmits the K2 byte to the opposite station. The opposite station sets a line number for a protection line in the K2 byte, and transmits the K2 byte to the own station. Such transmission and reception of K1 and K2 bytes are repeated until the failure is repaired. When it is detected that the failure is repaired, the own station stop transmitting an SF. However, since the own station is in a non-rev mode, the own station sets a DNR (Do Not Revert) in the K1 byte, and transmits the K1 byte to the opposite station. This means that the own station does not bridge back to the work line. On the other hand, since the opposite station in a rev mode, the opposite station waits for an NR for indicating that the failure of the work line is repaired. Under these circumstances, since instead of an NR which is transmitted when there is no failure a DNR is transmitted to the opposite station, mismatching between rev and non-rev modes occurs. Although what kind of process is executed depends on the design of the apparatus when the opposite station receives the DNR, in the worst case the line may be disconnected. Alternatively, as shown in the diagram, the opposite station may judge that the failure is not yet repaired, and may transmit a K2 byte with a line number for a protection line. Meanwhile, since the own station waits for a reply to the DNR, communication may be continued in a status where neither of the stations can ever get an expected reply. Alternatively, the status may be judged to be an error, and the bridging may get into trouble.
FIG. 4 explains the case where the own station is in a bi and rev mode, and the opposite station is in a bi and non-rev mode.
When there is no failure, an NR is exchanged between the own and opposite stations. When it is detected that there is a failure in the own station, the own station sets an SF in the K1 byte, and transmits the K1 byte to the opposite station. The opposite station bridges the work line and a protection line, sets a line number for the protection line to be bridged in the K2 byte, and transmits the K2 byte to the own station. It is in order to indicate in which direction the failure occurs that in this case the K1 byte transmitted from the opposite station is set to xe2x80x9c00100001xe2x80x9d, which is stipulated in ITU Recommendations mentioned earlier. When receiving the K1 and K2 bytes from the opposite station, the own station bridges the work line and a protection line, sets a line number of the bridged protection line and an SF in the K2 and K1 bytes, respectively, and transmits the K1 and K2 bytes to the opposite station. When receiving the K1 and K2 bytes, the opposite station verifies that the K1 and K2 bytes are designated by the bridged protection line, and returns the signal in which xe2x80x9c00100001xe2x80x9d for indicating failure information and the line number of the protection line are set in the K1 and K2 bytes, respectively, to the own station. When receiving the K1 and K2 bytes, the own station transmits a WTR (Wait To Restore) for commanding the opposite station to wait for the repair of the failure in the work line, and transmits the K1 bytes to the opposite station, since the own station is in a rev mode. At this time in the K2 byte the line number of the protection line is set. On the other hand, since the opposite station is in a non-rev mode, the opposite station waits for a signal with an SF set in the K1 byte. Therefore, when receiving the WTR, the bridging gets into trouble, since the opposite station receives an unexpected signal. Although what actually occurs depend on the design of the apparatus, both the own and opposite stations enter a status where an expected signal is never received. If, even when receiving the WTR, the opposite station holds the bridging status, the opposite station continues to transmit a signal in which failure information and the line number of the protection line are set in the K1 and K2 bytes, respectively, to the own station.
FIG. 5 explains the case where the own station is in a bi and non-rev mode, and the opposite station is in a bi and rev mode.
As described earlier, when there is no failure, an NR is set in the K1 byte, the K1 byte is exchanged, and thereby there is no problem. When it is detected in the own station that there is a failure in the work line, an SF is set in the K1 byte in the own station, and the K1 byte is transmitted to the opposite station. When receiving the K1 byte, the opposite station sets failure information and the line number of the protection line in the K1 and K2 bytes, respectively, and transmits the K1 and K2 bytes to the own station. When receiving the K1 and K2 bytes, the own station bridges the work line and a protection line. Then, the own station sets an SF and the line number of a protection line in the K1 and K2 bytes, and transmits the K1 and K2 bytes to the opposite station. Then, the exchange of such signals is continues until the failure is repaired. When the failure is repaired, since the own station is in a non-rev mode, it sets a DNR for requesting not to bridge back to the work line in the K1 byte, and transmits the signal to the opposite station. However, since the opposite station is in a rev mode, the opposite station waits to receive a WTR. Thus, a mismatching of mode occurs. Although what kind of problem is caused by this mismatching of mode depends on how the actual apparatus is designed, in the worst case signals are disconnected. When the opposite station is configured so as to hold the bridging status as it is after receiving the DNR, as shown in the diagram, failure information and the line number of the protection line are set in the K1 and K2 bytes, respectively, and the signal is transmitted to the own station.
FIG. 6 explains the case where the own station is in a uni and rev mode, and the opposite station is in a bi and rev mode.
When a failure is detected in the own station, the information is transmitted to the opposite station as the SF of the K1 byte. Since the opposite station is in a bi mode, the opposite station bridges the work and protection lines, and transmits an RR (Reverse Request) being a request for bridging to the own station. When receiving the RR, the own station reads the protection line number in the K1 byte, and bridges the work and protection lines. Since the own station is in a uni mode, the own station sets an SF for indicating that the work line out of order in the K1 byte, and transmits the signal to the opposite station. Although the opposite station waits for the signal from the own station in which the line number of the protection line is set in the K2 bytes, in the K2 byte the same line number as the K2 byte transmitted from the opposite station together with the RR is not set, since the own station is in a uni mode. Therefore, a channel (ch) mismatching occurs, and after a predetermined time (50 milli-seconds later) an alarm sounds. Since the opposite station is in a bi mode, the opposite station continues to wait for the signal in which the channel is set in the K2 byte. Meanwhile, since the own station is in a uni mode, the own station only continues to transmit an SF. This situation continues until the failure is repaired. When the failure is repaired, the own station bridges back between the work and protection lines (the own station is in a rev mode), and transmits an NR to the opposite station. When receiving the NR, the opposite station bridges back between the work and protection lines. Thus, the number of the line currently used by the K2 byte transmitted from the own station and the number of the line currently used by the K2 byte transmitted from the opposite station coincide with each other, and thereby the channel mismatching is solved. In this way, in the case of FIG. 6, a channel mismatching alarm continues to sound until the failure is repaired. Even in this case, there is a possibility that the bridging status gets into trouble due to a channel mismatching.
FIG. 7 explains the case where the own station is in a bi and rev mode, and the opposite station is in a uni and rev mode.
As described earlier, when there is no failure, an NR is exchanged between the own and opposite stations. When a failure is detected in the own station, a K2 byte with an SF is transmitted from the own station. When receiving the K2 byte, the opposite station sets the line number of the protection line to be used in the K2 byte, and returns the K2 byte to the own station. Since the opposite station is in a uni mode, there is no problem. Meanwhile, since the own station is in a bi mode, the own station waits for an RR from the opposite station. However, since nothing is set in the K1 byte transmitted from the opposite station, a channel mismatching occurs on the own station side, and after a predetermined time (50 milli-seconds in the case of FIG. 7) an alarm sounds. Although the own station continues to transmit an SF to the opposite station, the opposite station continues to transmit a signal in which xe2x80x9c0sxe2x80x9d and the line number are set in the K1 and K2 bytes, respectively, to the own station, since the opposite station is in a uni mode. This situation continues until the failure is repaired.
When the repair of the failure is detected in the own station, the work line is restored to normal conditions, an NR is transmitted from the own station, and thereby the channel mismatching is solved. The opposite station receives an NR from the own station, and transmits an NR to the own station.
In this way, since on the own station side the failed work line is bridged by a protection line, the own station waits for an RR from the opposite station. However, since the RR is never transmitted, the own station cannot bridge the lines. Accordingly, an APS unit cannot operate normally due to the channel mismatching.
FIG. 8 explains the case where the own station is in a uni and non-rev mode, and the opposite station is in a bi and non-rev mode.
When there is no failure, an NR is exchanged between the own and opposite stations. When a failure is detected in the own station, an SF is set in the K1 byte in the own station, and the K1 byte is transmitted from the own station. When receiving the K1 byte, the opposite station bridges the lines on the transmitting side, sets an RR and the protection line number in the K1 and K2 bytes, respectively, and transmits the K1 and K2 bytes to the own station. The own station reads the protection line number in the K2 byte transmitted from the opposite station, bridges the failed work line and a protection line, and transmits an SF to the opposite station. Since the opposite station is in a bi mode, the opposite station expects a signal of which the number of the bridged protection line is set in the K2 byte. However, since the own station is in a uni mode, the opposite station cannot get the expected signal. Accordingly, the opposite station judges that a channel mismatching occurs, and after a predetermined time an alarm sounds. Although the opposite station continues to transmit an RR hoping to get the expected reply, such a reply is not returned from the own station, and thereby the channel mismatching continues. When the repair of the failure is detected in the own station, a DNR is transmitted from the own station to the opposite station. However, as the line number of the bridged protection line is not still set in the K2 byte, the opposite station judges that the line of the line number designated by the opposite station is not bridged, and thereby the channel mismatching continues. In this case, the bridging status gets into trouble, and in the worst case there is a possibility that the signals may be disconnected.
FIG. 9 explains the case where the own station is in a bi and non-rev mode, and the opposite station is in a uni and non-rev mode.
When the occurrence of a failure is detected in the own station, K bytes (K1 and K2 bytes) transmitted from the own station change from NR to SF. When receiving the K bytes, the opposite station sets the line number of a protection line to be bridged in a K2 byte, and transmits the K2 byte to the own station. However, since the own station is in a bi mode, the own station waits for an RR. Accordingly, when the own station receives the K bytes from the opposite station, a channel mismatching occurs. Although the own station continues to transmit an SF until an RR is transmitted from the opposite station, the status where an RR cannot be received continues. When the repair of the failure is detected in the own station, the own station transmits a DNR, since the own station is in a bi and non-rev mode. However, since the opposite station waits for an NR, the bridging process does not operate normally, and thereby the channel mismatching continues.
As described above, since conventionally there are no mode settings of rev/non-rev and bi/uni in the K1 and K2 bytes, the own station cannot know the mode of the opposite station. Accordingly, there is a good possibility that an APS unit may not operate normally, such as the facts that a channel mismatching alarm sounds for ever, signals are disconnected depending on the design of an apparatus, etc.
It is an object of the present invention to provide a failure detection apparatus for detecting the mode of an opposite station and matching the mode of the own station with the mode of the opposite station in a synchronous communication network.
The terminal station of the present invention is a terminal station in a synchronous communication network where data are exchanged in units of frames including an overhead for storing a control signal, and is characterized in comprising an extraction unit for extracting information for indicating request contents needed to execute a process of automatically bridging a work line and a protection line from a received overhead, a mismatching judgment unit for judging a mismatching between the work/protection line bridging mode of a terminal station transmitting the information and the work/protection line bridging mode of the own terminal station by judging whether or not the request contents of the information are not used in the work/protection line bridging mode of the own terminal station, and an automatic bridging unit for matching based on the judgement result of the mismatching judgement unit the work/protection line bridging mode of the own terminal station with the work/protection line bridging mode of a terminal station transmitting the information.
The apparatus of the present invention is a mismatching detection apparatus for detecting the mismatching of an inter-station operation mode relating to an automatic work/protection line bridging process provided in terminal stations in a SONET or SDH communication network, and is characterized in comprising a comparison unit for judging whether or not a predetermined request relating to the work/protection line bridging process is set in K bytes extracted from signals received by the own terminal station, and a mode judgement unit for comparing the operation mode of a terminal station transmitting the signal which is obtained from the judgement result of the comparison unit with the operation mode of the own terminal station, judging whether or not both operation modes coincide with each other, and outputting the result of the judgement.
The method in the first aspect of the present invention is an operation mode mismatching judging method for terminal stations in a synchronous communication network where data are exchanged in units of frames including an overhead for storing a control signal, and is characterized in comprising (a) a step of extracting information indicating request contents needed to execute a process for automatically bridging a work line and a protection line from a received overhead, (b) a step of judging a mismatching between the work/protection line bridging mode of a terminal station transmitting the information and the work/protection line bridging mode of the own terminal station by judging whether or not the request contents of the information are not used in the work/protection line bridging mode of the own terminal station and (c) a step of matching based on the judgement result of step (b) the work/protection line bridging mode of the own terminal station with the work/protection line bridging mode of a terminal station transmitting the information.
The method in the second aspect of the present invention is a mismatching detecting method for detecting the mismatching of an inter-station operation mode relating to an automatic work/protection line bridging process provided in terminal stations in a SONET or SDH communication network, and is characterized in comprising (a) a step of judging whether or not a predetermined request relating to the work/protection line bridging process is set in K bytes extracted from signals received by the own terminal station and (b) a step of comparing the operation mode of a terminal station transmitting the signal which is obtained from the judgement result of the step (a) with the operation mode of the own terminal station, judging whether or not both operation modes coincide with each other, and outputting the result of the judgement.
According to the present invention, the mode of an opposite station can be detected by judging whether or not the contents of transmitted information are unique to a specific operation mode even if information on the operation modes of both terminal stations executing the bridging process is not set in information for an automatic work/protection line bridging process provided in the overhead of a frame exchanged between terminal stations through a synchronous communication network. Thus, it can be known whether or not there is a mode mismatching by comparing the detected operation mode of the opposite station with the operation mode of the own station. Thus, the supervisor of the network can operate so as to match the modes of both terminal stations. A terminal station itself can automatically solve the mismatching of an operation mode between the opposite station and the own station by modifying the operation mode of the own station.
Accordingly, inconveniences due to the design of an actual apparatus such as the continuation of alarm sounding, the disconnection of signals, etc. due to the mismatching of operation modes can be avoided. Even when two terminal stations in communication are manufactured by different makers, unexpected inconveniences due to the mismatching of operation modes can be avoided by a work/protection line bridging process and can continue to be normally operated.